Modern-day machinery has integrated all phases of the crop harvesting process. Though typically thought of as one unit, a combine actually comprises three sections: a header for gathering, cutting, and consolidating the crop material; a feeder for conveying the consolidated crop from the header to a thresher-separator; and a thresher-separator for removing and separating the crop from the plant material.
Within the header itself are typically four components: a longitudinal divider on each side of the header which partitions the crop to be cut during the current swath from that to be cut during future swaths, and biases said crop either toward or away from a cutter; a transverse reciprocating cutter which severs the plant at or near ground level; a transverse reel which feeds the standing crop into the cutter and the severed crop into a rearwardly located transverse trough; and a transverse auger which consolidates the crop at some point along its length and delivers the crop into the feeder.
During harvesting operations, a change in crop conditions may necessitate repositioning the reel relative to the cutter or dividers to prevent grain losses. However, as header widths have increased in response to demands for increased capacity machinery, reel mass has correspondingly increased whereby it no longer is feasible for operators to manually reposition the reel without the aid of a mechanically advantaged device. Simple devices enabling such adjustments are not new to the art as seen in U.S. Pat. Nos. 2,387,069, and 3,283,487. U.S. Pat. No. '069 teaches a mechanical means for vertical reel adjustment, and a screw means for fore and aft reel adjustment. U.S. Pat. No. '487 teaches similar adjustments using a hydraulic means, but does not describe hydraulic circuitry or address problems of equalization or phasing between the pair of cylinders mounted on oppposite sides of the reel. Experience has shown that such problems do arise, especially with serially connected hydraulic cylinders.
Leakage rates past piston seals of new double-acting hydraulic cylinders typically fall within a narrow range. However, as the piston seals wear differently with usage due to nonuniform cylinder wall finishes, dimensional inaccuracies, oil contamination, etc., their leakage rates will variously increase. If two cylinders having dissimilar leakage rates are serially connected, such as in the application under consideration, one cylinder will continually attempt to lead or lag the other, thereby creating an undesirable skew in the header reel. Furthermore, replacing any of the serially connected hydraulic cylinders, fittings or hoses will also affect the phasing. It therefore becomes desirable to have a convenient means to occasionally rephase the pistons.
One conventional phasing technique utilizes a combination of an orifice inlet and a main inlet located within each cylinder port, whereby only the orifice inlet is positioned to allow restricted flow between the two cylinder ports subsequent to the piston reaching either full extended or retracted stroke position. Such flow provides the volumetric means for phasing all downstream serially connected cylinders in a likewise full-stroke position. A disadvantage of this technique becomes apparent when the piston is initially stroked in a direction away from its fully stroked position. The initial movement of said piston is dependent upon a pressure differential across the orifice inlet, through which undesirably passes a portion of the fluid flow supplied for actuation of the piston. As fluid viscosity changes, especially with temperature changes, the flow required to achieve an adequate pressure differential across the orifice inlet to initiate piston movement increases. Similarly, as the piston load increases, so must the pressure differential across the orifice inlet, and therefore the fluid flow. The operator must therefore vary the fluid flow to correspond to conditions. If the operator has increased his flow to compensate for a lowered viscosity oil, the piston travel rate may be unacceptably great, especially with small bore cylinders typically used in such applications.
There thus exists a need for hydraulic circuitry which achieves phasing of a plurality of serially connected cylinders and which eliminates the dependency upon sufficient fluid flow to initiate piston travel opposite its fully-stroked position.